What I would do for basic installation. Rx from panel to jbox. From there 1/2" PVC to a wp switch box with a single pole switch mounted to a 4x4 post, above that wp box with a 20 amp twistlock recept. Run bond around pool to motor,install gfi breaker. Also I wouldinstall a general use gfi on the house to comply with 680-6a. Price tag materials $150 Labor 5 hours @ $65.00 permit $75 total $550.00
Hey, try 3/4" rigid for the underground, less depth always. 3/4" is my minimum UG feeds for any distance and even 2/3 wires, always makes life easier now and in the future. Bring the feed into the bottom of your box, and in the next hole in the box is my 3/4" rigid beat into the ground 5/6' for stability, very clean install, and some additional grounding help. I always use double boxes and deep. If you feel like it, back-up two single deep boxes, switch on back, outlet facing pool. Careful of the general use GFI rule though.Typically don't use GFI breakers due to cost, usually use a faceless next to general use GFI.
Running 3/4" cndt is good advice. Also, consider running the next size up wire (or calculate it). In your case your only going 20ft from the house - not bad.
In some cases it the run could be a couple of hundred feet - if the service panel is on the other side of the house and you have to go around a few things on the way to the pool pump. This all has to do with voltage drop. Many homes have low voltage at the service drop already. It can be within ANSI spec and still be too low to allow you to drop much more and still serve high loads.
I like the GFI C/B idea myself, rather than the GFCI outlet. Even if the GFCI outlet trips, you still have non-protected conductors present in the box. As badly as homeowners can beat up a w/p cover and gasket....well, you see.